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Re: [PATCH] Use direct I/O for loop devices
- To: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 18 Aug 2022 09:02:11 +0200
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- Cc: Wei Liu <wl@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Xen developer discussion <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 18 Aug 2022 07:02:22 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.08.2022 22:46, Demi Marie Obenour wrote:
> This is a huge performance improvement for two reasons:
>
> 1. It uses the filesystem’s asynchronous I/O support, rather than using
> synchronous I/O.
> 2. It bypasses the page cache, removing a redundant layer of caching and
> associated overhead.
> ---
> tools/hotplug/Linux/block | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/hotplug/Linux/block b/tools/hotplug/Linux/block
> index
> 2691b56951c9b82094471a141b9e0bed04abb929..75785f3a5422c4a5f962a4cd4f6acae5080d036d
> 100644
> --- a/tools/hotplug/Linux/block
> +++ b/tools/hotplug/Linux/block
> @@ -330,7 +330,7 @@ mount it read-write in a guest domain."
> else
> roflag=''
> fi
> - do_or_die losetup $roflag "$loopdev" "$file"
> + do_or_die losetup --direct-io=on $roflag "$loopdev" "$file"
I guess you want to first check (maybe in tools/configure) that losetup
actually supports that option. The old-ish one I'm looking at doesn't,
according to its --help output at least.
Jan
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